U.S. patent number 6,124,041 [Application Number 09/266,338] was granted by the patent office on 2000-09-26 for copper-based paste containing copper aluminate for microstructural and shrinkage control of copper-filled vias.
This patent grant is currently assigned to International Business Machines Corporation. Invention is credited to Farid Youssif Aoude, Lawrence Daniel David, Renuka Shastri Divakaruni, Shaji Farooq, Lester Wynn Herron, Hal Mitchell Lasky, Anthony Mastreani, Govindarajan Natarajan, Srinivasa S. N. Reddy, Vivek Madan Sura, Rao Venkateswara Vallabhaneni, Donald Rene Wall.
United States Patent |
6,124,041 |
Aoude , et al. |
September 26, 2000 |
Copper-based paste containing copper aluminate for microstructural
and shrinkage control of copper-filled vias
Abstract
A copper-based paste is disclosed for filling vias in, and
forming conductive surface patterns on, ceramic substrate packages
for semiconductor chip devices. The paste contains copper aluminate
powder in proper particle size and weight proportion to achieve
grain size and shrinkage control of the via and thick film copper
produced by sintering. The shrinkage of the copper material during
sintering is closely matched to that of the ceramic substrate.
Inventors: |
Aoude; Farid Youssif
(Wappingers Falls, NY), David; Lawrence Daniel (Wappingers
Falls, NY), Divakaruni; Renuka Shastri (Ridgefield, CT),
Farooq; Shaji (Hopewell Junction, NY), Herron; Lester
Wynn (Hopewell Junction, NY), Lasky; Hal Mitchell (Hyde
Park, NY), Mastreani; Anthony (Hopewell Junction, NY),
Natarajan; Govindarajan (Pleasant Valley, NY), Reddy;
Srinivasa S. N. (LaGrangeville, NY), Sura; Vivek Madan
(Hopewell Junction, NY), Vallabhaneni; Rao Venkateswara
(Wappingers Falls, NY), Wall; Donald Rene (Wappingers Falls,
NY) |
Assignee: |
International Business Machines
Corporation (Armonk, NY)
|
Family
ID: |
25053958 |
Appl.
No.: |
09/266,338 |
Filed: |
March 11, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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758991 |
Sep 10, 1991 |
5925443 |
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Current U.S.
Class: |
428/472;
257/E23.075; 428/209; 428/323; 428/325; 428/469; 428/697;
428/901 |
Current CPC
Class: |
H01L
21/486 (20130101); H01L 23/49883 (20130101); H05K
1/092 (20130101); H01L 2924/09701 (20130101); H05K
3/4611 (20130101); Y10S 428/901 (20130101); Y10T
428/24917 (20150115); H01L 2924/0002 (20130101); Y10T
428/25 (20150115); Y10T 428/31678 (20150401); Y10T
428/252 (20150115); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
H01L
21/02 (20060101); H01L 21/48 (20060101); H01L
23/498 (20060101); H01L 23/48 (20060101); H05K
1/09 (20060101); H05K 3/46 (20060101); H01B
001/06 () |
Field of
Search: |
;428/209,428,457,469,472,323,325,901,697 ;252/512,518 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0272129 |
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Dec 1987 |
|
EP |
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63-095182 |
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Apr 1988 |
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JP |
|
Primary Examiner: Turner; Archene
Attorney, Agent or Firm: Blecker; Ira D.
Parent Case Text
This application is a continuation of U.S. patent application Ser.
No. 07/758,991 entitled "COPPER-BASED PASTE CONTAINING COPPER
ALUMINATE FOR MICROSTRUCTURAL AND SHRINKAGE CONTROL OF
COPPER-FILLED VIAS", filed Sep. 10, 1991, and now issued as U.S.
Pat. No. 5,925,443.
Claims
What is claimed is:
1. A multilayered ceramic package comprising:
a ceramic substrate; and a copper-based sintering paste for forming
conductive vias and surface patterns in or on said ceramic
substrate, said paste comprising:
powdered copper particles consisting of elemental copper, powdered
copper aluminate particles and organic materials, said copper
aluminate constituting up to 10% by weight of said paste, wherein
the copper for said copper-based sintering paste comes exclusively
from said powdered copper particles and said powdered copper
aluminate.
2. The ceramic package defined in claim 1 wherein said copper
aluminate in said sintering paste constitutes up to 3% by weight of
said paste.
3. The ceramic package defined in claim 1 wherein said copper
aluminate in said sintering paste is present as a minimum in a
small but effective amount to control shrinkage of said paste.
4. The ceramic package defined in claim 1 wherein said copper
aluminate in said sintering paste constitutes 0.02-10% by weight of
said paste.
5. The ceramic package defined in claim 4 wherein said copper
aluminate constitutes 0.02-3% by weight of said paste.
6. The ceramic package defined in claim 5 wherein said copper
aluminate constitutes 0.02-1% by weight of said paste.
7. The ceramic package defined in claim 6 wherein said copper
aluminate constitutes 0.2-1% by weight of said paste.
8. The ceramic package defined in claim 7 wherein the average size
of said copper aluminate particles is not greater than 3.0
micrometers.
9. The ceramic package defined in claim 7 wherein the average size
of said copper particles is about 5-8 micrometers.
10. The ceramic package defined in claim 1 wherein in said
sintering paste said copper aluminate constitutes 0.2-1% weight of
said paste,
the average size of said copper aluminate particles is not greater
than about 3.0 micrometers, and
the average size of said copper particles is about 5-8 micrometers.
Description
BACKGROUND OF THE INVENTION
The present invention generally relates to copper-filled vias in
ceramic substrates and, more particularly, to a copper-based paste
containing copper aluminate powder in proper particle size and
weight proportion for grain size and shrinkage control of the via
and thick film copper produced by sintering.
The use of copper-filled vias in ceramic substrates and sintering
processes for producing them are well known in the semiconductor
packaging art as taught, for example, in U.S. Pat. No. 4,234,367,
issued on Nov. 18, 1980 to Lester W. Herron et al. and assigned to
the present assignee, the disclosure of which is incorporated by
reference herein. Recently, more interest has been focused on the
associated problems of the disparity in shrinkage rates between
copper and ceramic as well as the onset of via "opens",
particularly as via diameters are reduced below 100 .mu.m in high
circuit density applications. A discussion of such problems is
given in U.S. Pat. No. 4,776,978, issued on Oct. 11, 1988 to Lester
W. Herron et al. and assigned to the present assignee, the
disclosure of which is incorporated by reference herein.
As set forth in the cited U.S. Pat. No. 4,776,978, metal particles,
such as copper, in the via paste undergo sintering with attendant
shrinkage of the thick film pattern (also consisting of the paste)
during the initial phase of the sintering cycle whereas the ceramic
and glass particles (of the ceramic substrate containing the vias)
undergo sintering during the intermediate and final phases of the
sintering cycle along with their characteristic shrinkage. One
method of delaying the onset of sintering of the metal particles
until at least the intermediate phase of the sintering cycle is to
intersperse the metal particles in the thick film with a high
melting point material such as aluminum oxide.
Although the foregoing generalized considerations have been known
in the art for some time and have provided the basis for techniques
for overcoming previous shrinkage and related problems, more
refined and detailed approaches are required to meet the needs of
copper-filled vias in ceramic substrates with increasing circuit
densities and the concomitant via diameters in the range of about
85 to 100 .mu.m. It is also desirable to provide a copper paste
mixture which can be adapted for use with the next generation of
ceramic packages which exhibit reduced shrinkage from
sintering.
The following references illustrate previous techniques attempting
to overcome shrinkage and other problems.
U.S. Pat. No. 4,594,181, issued on Jun. 10, 1986 to Vincent P.
Siuta, teaches the dispersal of copper particles in a solution of
an organometallic compound in an anhydrous volatile organic solvent
towards obtaining a better shrinkage match of copper to ceramic
substrate during sintering.
U.S. Pat. No. 4,599,277, issued on Jul. 8, 1986 to James M.
Brownlow et al., discloses the addition of an organometallic
compound to a metal member such as copper paste which compound
undergoes decomposition during sintering to provide a coating such
as aluminum oxide on the copper particles towards obtaining better
shrinkage match between copper and ceramic substrate during
sintering.
Published European Patent Application, Publication No. 0272129,
published Jun. 22, 1988 by Hitoshi Suzuki et al., describes a paste
composition including a copper powder and an organometallic
compound such as an organoaluminate compound, towards obtaining
improved adhesion strength of sintered copper to a ceramic
substrate.
U.S. Pat. No. 4,906,405, issued on Mar. 6, 1990 to Seiichi Nakatani
et al. and Japanese Patent J63095182, issued on Apr. 26, 1988 to
Goei Seisakusho KK, teach a paste made of copper oxide, and
CuAl.sub.2 O.sub.4 as an additive towards obtaining improved
adhesion strength of sintered copper to a ceramic substrate.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a copper paste
with appropriate additive to produce copper grain size in the range
of about 5 to 15 .mu.m after sintering.
Another object is to provide a copper paste with an appropriate
additive to substantially match the shrinkage of the resulting
copper material to the shrinkage, if any, during sintering of a
ceramic substrate having vias filled with said copper paste.
A further object is to provide a copper paste with an appropriate
additive to provide substantially reduced shrinkage after sintering
of the copper material in low shrinkage porous ceramic substrates
having vias filled with said copper paste.
These and other objects of the present invention, as will be seen
from a reading of the following specification, are achieved in a
preferred embodiment of the present invention by the provision of a
copper paste comprising copper powder, up to about 10 weight
percent copper aluminate powder, and the remainder organic
material. Use of copper aluminate in one preferred range from about
0.4 to about 1 weight percent provides the dual benefits of grain
size control as well as shrinkage matching control of the via
copper during sintering.
It is preferred that the size of the copper aluminate particles be
in the range of about 3.0 .mu.m or less because the amount of
copper aluminate required for grain size control of the sintered Cu
varies inversely with copper aluminate particle size.
In a preferred embodiment of the invention, glass-ceramic particles
are added to the copper-based paste to provide a shrinkage match
during sintering that is substantially identical to that of a
glass-ceramic substrate.
DETAILED DESCRIPTION OF THE INVENTION
Multilayered glass-ceramic packages for supporting and
interconnecting microelectronic chip devices can be sintered to a
peak temperature greater than 950.degree. C. Because of the high
temperatures, the chip interconnecting copper conductors tend to
experience exaggerated grain growth in the vias and in the thick
film copper wiring lines.
The growth of large grains in copper is not desirable from the
point of view of reliability. The reason for this is that the
plasticity of copper varies with the orientation of two neighboring
large copper grains and the grains may separate when they are
cooled down from high temperature and on subsequent thermal
cycling. Inasmuch as the conductor size in both the vias and
surface lines is about 70-100 .mu.m, it is desirable to keep the
copper grain size after sintering as small as possible, namely
about 5-15 .mu.m.
In accordance with a first aspect of the present invention, copper
grain size is minimized in a sintering cycles such as the one
disclosed in the aforementioned U.S. Pat. No. 4,234,367. Copper
grain size is minimized by adding a small amount of copper
aluminate powder to copper powder, mixing with suitable organics to
form a paste, and then screening the paste using a mask on to a
green sheet. The green sheet may comprise a variety of materials
including, but not limited to, mullite, borosilicate glass,
cordierite glass, ceramic, etc. The cordierite glass ceramic
materials, such as that disclosed in Kumar et al. U.S. Pat. No.
4,301,324, the disclosure of which is incorporated by reference
herein, are preferred. Preferably, the copper powder has an average
particle size of about 5-8 .mu.m and the copper aluminate powder
has an average particle size of about 3.0 .mu.m or less.
There are two forms of copper aluminate, namely cupric aluminate
(CuAl.sub.2 O.sub.4) and cuprous aluminate (CuAlO.sub.2). Unless
specifically stated otherwise, whenever copper aluminate is
mentioned in this specification, it should be understood that
copper aluminate is being used in the generic sense to include
cupric aluminate and cuprous aluminate, both of which should be
considered to be within the scope of the present invention.
When suitable conditions are present in a sintering cycle such as
taught in the U.S. Pat. No. 4,234,367, copper aluminate decomposes
into copper and alumina according to the following reactions:
The alumina particles produced by the foregoing decomposition
reactions are very small, submicron in size, and are distributed
inside the copper matrix. The presence of a small amount of
porosity and the small alumina particles inside the copper matrix
have been found to inhibit copper grain growth and result in small
copper grains after sintering at high temperature in excess of
950.degree. C.
More particularly, the unique use of powdered copper aluminate in
the copper paste, in accordance with the present invention, has the
special property of yielding grain size control of the sintered
copper.
By adding powdered copper aluminate to copper paste, preferably in
the range 0.2-1.0% by weight, the sintered copper grain size can be
kept small. More importantly, the maximum grain size can be kept
under about 20 .mu.m, which improves the reliability of multilayer
ceramic packages having copper conductors. It should be noted that
by decreasing the particle size of the copper aluminate powder,
smaller copper grain sizes can be obtained with lower weight
percentage additions of the copper aluminate to the copper
paste.
In general terms, grain size control is the predominant effect when
the powdered copper aluminate paste additive is present up to about
1 weight percent. Grain size control aids in avoiding opens
(breaks) in the sintered copper vias and circuits which have been
experienced using other paste additives which produce much larger
copper grain sizes after sintering.
It has been found that additions to the sintering paste of copper
aluminate up to about 10 weight percent are useful for controlling
the shrinkage of the sintered copper. With increasing amounts of
copper aluminate, but not greater than about 10 weight percent, the
sintered copper becomes porous, i.e., the copper particles continue
to shrink microscopically but not on a macro (global) scale. At
about 10 weight percent copper aluminate, the copper no longer
undergoes shrinkage upon sintering. It is more preferred that the
copper aluminate be kept at about 3 weight percent or less since at
higher amounts of copper aluminate, the sintered copper has lower
strength and increased electrical resistivity.
It has further been found that shrinkage control is possible when
there is present, as a minimum, a small but effective amount of
copper aluminate. The lower limits have not been determined yet
with precision. It is known that about 0.01 weight percent of
alumina will induce shrinkage control. It is assumed, therefore,
that amounts of copper aluminate (about 0.02 weight percent) that
will yield about 0.01 weight percent alumina will also achieve
similar shrinkage control, given similar particle sizes. Smaller
amounts of copper aluminate are likely to be effective if the
particle size of the copper aluminate, now at about 3.0 .mu.m, is
reduced further.
As is apparent, the effects of grain size control and shrinkage
control may advantageously overlap at small amounts of copper
aluminate additions.
It would be most desirable to match or substantially match
shrinkage characteristics during sintering of the copper vias and
lines with that of a glass-ceramic, particularly a cordierite
glass-ceramic, material. Thus, in a preferred embodiment of the
invention, there is proposed a copper-based sintering paste
comprising copper particles, glass-ceramic particles, copper
aluminate, and suitable organic binder materials. Based on volume
percent of the inorganic solids, the paste comprises about 90
volume percent copper particles, about 5 to 12 volume percent
glass-ceramic particles and about 0.3-1.5 volume percent copper
aluminate.
It is preferred that the copper particles have a bimodal
distribution. Although a unimodal distribution of the copper
particles (preferably having an average particle size of 5-8 .mu.m)
will also work well. More
preferably, there should be about 60-90 volume percent copper
particles having an average particle size of 5 to 6 .mu.m and 0-30
volume percent of copper particles having an average particle size
of 1.5 to 2.0 .mu.m. Also preferably, the copper aluminate
particles should have an average particle size of 0.7 to 3.0
.mu.m.
It is anticipated that the present invention will have
applicability to many glass-ceramic materials. The preferred
glass-ceramic materials, however, are the cordierite glass-ceramics
disclosed in the Kumar et al. U.S. Pat. No. 4,301,324. The average
particle size of the glass-ceramic particles should be about 3.5
.mu.m.
The advantages of the present invention will become more apparent
after referring to the following examples.
EXAMPLES
Examples I
A series of samples were prepared comprising copper particles and
varying amounts of copper aluminate in order to determine the
efficacy of copper aluminate as a grain size control agent.
Batches of copper powder particles (from Metz Metallurgical and
Dupont), having an average particle size of 6 .mu.m, were mixed
with copper aluminate (CuAl.sub.2 O.sub.4), having an average
particle size of about 2.5 .mu.m, and various paste additives,
including ethyl cellulose resin plus a solvent, wetting agent, and
flow control agent. Each batch was dried in an oven at about
100.degree. C. and then milled in a rod mill for 1-2 hours.
Thereafter, the paste was pressed into pellets at about 5000 psi.
Finally, the pellets were sintered in a sintering cycle such as
that disclosed in the above Herron et al. U.S. Pat. No.
4,234,367.
The pellets were examined for grain size and the results are
illustrated in Table I. As can be seen, the grain size is markedly
reduced when at least 0.2 weight percent copper aluminate is
present in the paste.
TABLE I ______________________________________ Weight % Copper
Average Grain Maximum Grain Aluminate In Size in Copper Size In
Copper Paste (.mu.m) (.mu.m) ______________________________________
0 18 53 0 >20 >100 0.2 13 55 0.4 13 41 0.5 9 18 0.6 8 15 0.8
8 19 1.0 7 14 ______________________________________
The pellets were also examined for densification, noted as percent
of theoretical density, and resistivity. The results are
illustrated in Table II. The samples listed in Table II only used
the Metz copper powder particles. As can be seen, there is a steady
decline in percent theoretical density achieved with increasing
amounts of copper aluminate, thus illustrating the ability to
control the shrinkage of the sintered copper.
TABLE II ______________________________________ Weight % Copper %
of Theoretical Resistivity Aluminate in Paste Density .mu.-ohm-cm
______________________________________ 0.3 93 0.4 91 2.2 1.0 80 2.9
1.2 76 3.1 2.0 73 3.0 69 10.0 55
______________________________________
Examples II
Samples were prepared comprising copper particles, copper aluminate
particles and glass-ceramic particles in order to determine whether
it is possible to match the shrinkage characteristics during
sintering of a copper paste and a glass-ceramic material.
A batch of copper-based paste was prepared having the following
composition, by volume percent of inorganic materials: 10.08 volume
percent of copper (from Metz Metallurgical) having an average
particle size of 1.5 .mu.m, 79.26 volume percent of copper (from
Metz Metallurgical) having an average particle size of 6 .mu.m, 9.9
volume percent of cordierite glass-ceramic particles (average
particle size of 3.5 .mu.m) of the composition listed in Table III,
and 0.76 volume percent of copper aluminate having an average
particle size of 0.6 .mu.m. To this mixture was added various past
additions, including ethyl cellulose resin plus a solvent, wetting
agent, and flow control agent. The resulting mixture was dried in
an oven at about 100.degree. C. and then milled in a rod mill for 1
to 2 hours. Thereafter, the paste was pressed into pellets at about
5000 psi.
TABLE III ______________________________________ Glass-ceramic in
Substrate Glass- paste, weight % Ceramic, weight %
______________________________________ 55.0 SiO.sub.2 55.0 21.23
Al.sub.2 O.sub.3 21.1 20.0 MgO 22.3 1.0 B.sub.2 O.sub.3 1.3 2.77
P.sub.2 O.sub.5 0.3 ______________________________________
Next, a batch of glass-ceramic material (average particle size 3.5
.mu.m) representative of glass-ceramic material in substrates was
prepared. The composition is also listed in Table III. The
glass-ceramic material was prepared in a conventional way such as
that disclosed in the Herron et al. U.S. Pat. No. 4,234,367, and
then pressed into pellets.
Both sets of pellets were sintered according to the sintering cycle
disclosed in the above Herron et al. patent as modified by Farooq
et al. U.S. patent application Ser. No. 07/672,517, filed Mar. 20,
1991, the disclosure of which is incorporated by reference
herein.
Generally speaking, the sintering cycle proceeds as follows. The
temperature was ramped up to 715.degree. C. in an atmosphere of 70%
water vapor/30% N.sub.2 followed by binder burnoff in a steam
ambient. Subsequently, the atmosphere was replaced with a forming
gas atmosphere and then the temperature was ramped up to
975.degree. C. in N.sub.2. The atmosphere is then changed to a
steam ambient and heating at 975.degree. C. continued to complete
the second step. The pellets were then cooled down, first in the
steam ambient and then in N.sub.2.
The shrinkage behavior of the pellets was measured during the
sintering cycle by a Netzsch dilatometer. It was observed that the
glass-ceramic pellets (representing the substrate) began to shrink
at about 800.degree. C. and stopped shrinking at about 860.degree.
C., while the paste pellets began to shrink at about 800.degree. C.
and stopped shrinking at about 890.degree. C. Thus, both sets of
pellets exhibited nearly identical shrinkage behavior. According to
the invention, therefore, shrinkage matching of paste and substrate
materials is obtained.
As is now apparent, the copper-based sintering paste comprising
copper aluminate proposed by the present inventors has fulfilled
the dual objectives of controlling the grain size in the sintered
copper while also altering the shrinkage behavior of the copper
particles.
It will be apparent to those skilled in the art having regard to
this disclosure that other modifications of this invention beyond
those embodiments specifically described here may be made without
departing from the spirit of the invention. Accordingly, such
modifications are considered within the scope of the invention as
limited solely by the appended claims.
* * * * *